1. Field of the Invention
The present invention is related generally to the field of internal combustion engine exhaust gas recirculation (EGR) for emissions improvement. More particularly, the invention provides a turbocharger compressor wheel having impeller vanes mounted on a side opposite the compressor impeller to act as an EGR pump with a separate diffuser and volute for EGR flow output from the pump and a separate scroll inlet to the EGR pump for recirculating exhaust gas in the charge air for the engine.
2. Description of the Related Art
EGR is a known method for reducing the NOX emissions in internal combustion engines. For effective use, an EGR system must overcome the adverse pressure gradient created by a positive pressure gradient across the engine which is typical of modern high efficiency diesel engines in at least a portion of their operating range. Various approaches to implementing EGR have included pumping of a portion of the exhaust gas from the exhaust manifold to the intake manifold. Pumping has been accomplished by introducing the exhaust gas into the compression inlet of a conventional turbocharger or supercharger present on the engine or, alternatively, providing a separate compressor receiving the exhaust gas and pressurizing it to a suitable pressure for insertion into the charge air downstream of the charge air boosting system on the engine. Some fuel consumption penalty is generally incurred by these systems.
In addition to pumping of EGR gases, control of back pressure in the exhaust system may be required to achieve desired system performance by enhancing the pumping capability and, if EGR is modulated or turned off, air fuel ratio control for the engine is desirable to maintain optimum engine performance.
The components and features of an EGR system must be accommodated within the constraints of limited volume available for allocation in modern engine compartments. It is, therefore, desirable to provide a highly integrated EGR system employing pumping components for recirculation of exhaust gas in close physical and functional cooperation with existing engine system components such as a turbocharger and providing exhaust back pressure and air fuel ratio control within the integrated system.